Video motion detectors have been proposed for detecting moving objects based on changes between subsequent images. More specifically typical proposed systems incorporate a background model and identify objects based on changes between a current image and the background model. However, in addition to true moving objects, many changes between subsequent images are caused by changes in lighting. These include, for example, turning lights on or off, passing clouds casting shadows, moving lights such as car headlights shining on objects or background, and the changing position of the sun. The appearance of background objects can change dramatically due to slight changes in orientation with respect to a source of light. For example slight rotations of leaves of plants with respect to a light source or slight movements of highly reflective surfaces such as waves on water. In addition, light changes may be due to automatic adjustments of a video camera such as adjustment of the iris or adjustment of the gain of the video signal.
Systems have been proposed that determine whether changes between images are caused by a change in lighting or the motion of objects based on normalized cross correlation NCC between the background model and the current image.
Those skilled in the art are directed to the following references:    1. A. Elgammal, D. Harwood, L. Davis, “Non-Parametric Model For Background Subtraction”, Proc. ICCV '99 Framerate Workshop, 1999.    2. C. Stauffer, W. E. L Grimson, “Adaptive Background Mixture Models For Real-Time Tracking”, Proc. IEEE conf. on Computer Vision and Pattern Recognition, 1999.    3. K. Dawson-Howe, “Active Surveillance Using Dynamic Background Subtraction”, Technical report TCD-CS-96-06, Dept. of Computer Science, Trinity College, Dublin, Ireland, 1996.    4. D. Toth, T. Aach, V. Metzer, “Illumination-Invariant Change Detection”, Proc. 4th IEEE Southwest Symposium on Image Analysis and Interpretation, 2000.    5. U.S. Pat. No. 6,031,934 to Ahmad et. al. “Computer Vision System For Subject Characterization” issued Feb. 29, 2000.
All the above references are hereby incorporated in whole by reference.